The invention relates to a control shaft of the camshaft adjusting unit for inlet valve shut-off in an internal combustion engine having adjusting cams which are spaced apart axially, and to the camshaft adjusting unit.
The inlet valve shut-off is a variant of a cylinder shut-off in internal combustion engines for reducing the fuel consumption. By means of deactivation of the inlet and outlet valves in combination with an interruption of the fuel supply, half of the cylinders are shut off, and the operating point of the engine is therefore shifted into a range of an improved degree of efficiency on account of the mean pressure increase.
In addition to mechanical solutions having more than one crankshaft, solutions for cylinder shut-off are also known from the prior art, for example, in which solutions the fuel injection and mixture ignition are enabled or shut off in a controlled manner.
A possible valve lift adjustment is also known from the prior art, which valve lift adjustment makes a continuous adjustment of the valve lift possible from minimum lifts as far as the maximum lift in a manner which is dependent on the respective load requirement of the internal combustion engine. In the known variable valve control systems, the cams of the camshaft act on an intermediate lever which opens and closes the inlet valves indirectly or directly. The intermediate lever is moved via a control shaft and, in particular, via adjusting cams which are configured on the control shaft in different operating positions, and the intermediate lever is pulled into an original position via a restoring spring. Depending on the operating position of the control shaft, the cams of the camshaft have a greater or lesser action on the intermediate lever and therefore adjust the valve lift which is achieved.
Building on what is known, the invention is based on the object of providing a cylinder shut-off via a special valve lift control, in particular a specially shaped control shaft for controlling the camshaft action.
This and other objects are achieved in accordance with embodiments of the invention.
According to the invention, a control shaft of a camshaft adjusting unit for an internal combustion engine is provided having adjusting cams which are spaced apart axially and are configured in a first axial section of the control shaft for continuous cylinder operation and in a second axial section for a cylinder shut-off. The adjusting cams for the continuous cylinder operation have a radial extent which is greater than a zero lift extent over their entire circumference of the cam circle. The adjusting cams for the cylinder shut-off have, in the circumferential direction, a shut-off section of the cam circle with a radial extent which is smaller than or equal to the zero lift extent. The control shaft has a stop which limits the rotation in both circumferential directions and serves as a calibration point for an engine electronics system. The system can therefore be recalibrated in the case of implausible values in the engine electronics system. The zero lift extent is defined as the radial extent of the adjusting cams as far as the base circle of the control shaft. In the case of a zero lift extent, the respective adjusting cam in the corresponding section exhibits no mechanical effect on other components and therefore prevents a valve lift.
An adjusting range of 30° of adjusting cam is left free for the mechanical stop, with the result that the adjusting range of the control shaft lies at 330°. In one possible embodiment, the stop is integrated into the bearing system of the control shaft. A pin can additionally be arranged on the control shaft, which pin comes into contact in the respective end positions with a lug which is seated on the bearing system, for example the bearing bracket.
In one advantageous embodiment, the mechanical stop is configured by way of two mechanical end stops which limit both rotational directions of the control shaft.
According to the invention, the cylinder shut-off is brought about by way of differently shaped adjusting cams on the control shaft, which control cams are configured in the case of the cylinders which are not to be shut off in such a way that opening of the inlet valves takes place in every position of the control shaft, and are configured in the case of the cylinders to be shut off in such a way that opening of the inlet valves (no shut-off) takes place in one position and no opening of the inlet valves takes place in a predefined shut-off position (shut-off). Cylinder filling and fuel injection do not take place in the case of inlet valves which are not open.
In one preferred embodiment, the control shaft for a straight six cylinder internal combustion engine is configured with, in each case, one adjusting cam per inlet valve, it being possible for three outer cylinders to be switched off, and the correspondingly associated adjusting cams being configured accordingly with a shut-off section with a radial extent as far as at most the base circle.
It is provided in one design variant in the case of the control shaft that it has a rotational adjusting range in the circumferential direction (in the cam circle) of from 330 to 360°. In the case of a 360° adjustability, the adjusting cams for the cylinder shut-off favorably have a radial extent which is consistently greater than a zero lift extent over the first 180° in the circumferential direction, and a radial extent which is consistently smaller than or equal to the zero lift extent over the second 180° in the circumferential direction. An extent smaller than the zero lift extent is to be considered as an exception, however, since the diameter of the control shaft is reduced greatly in the region of the adjusting cams as a result. The shape in the circumferential direction in the cam circle in the case of the adjusting cams for the cylinder shut-off is accordingly provided as a split in the circumferential direction. By way of the adjustment of the control shaft, the adjusting cams for the cylinder shut-off can be moved into a position, in which they exhibit no effect toward the outside on other components and the inlet valves remain closed. At the same time, the adjusting cams for the continuous cylinder operation take effect on account of their different shape and make the opening of the inlet valves possible. As a result of the axial split of the control shaft with partially provided adjusting cams for the continuous cylinder operation and adjusting cams for the cylinder switch-off, operation with all cylinders or only part of the cylinders is made possible depending on the control shaft rotational position.
The different positions of the control shaft are realized via an actuating motor. As a result of the split form of the adjusting cams for the cylinder shut-off, a rise in the torque occurs at the actuating motor. Said torque rise can be reduced by way of a special configuration of the adjusting cams for the continuous cylinder operation. For this purpose, it is provided in one variant of the invention that the adjusting cams for the continuous cylinder operation have a radial extent which is smaller than a maximum lift extent in a section of the cam circle, which section corresponds to the shut-off section of the adjusting cams for the cylinder shut-off. As a consequence, maximum valve lifts are not achieved during operation with partially shut-off cylinders. Said maximum valve lifts are scarcely required in any case in said operating phase, however.
The control shaft is distinguished by the fact that it can be set into at least two operating positions by way of rotation, the first operating position ensuring continuous cylinder operation in the case of all adjusting cams, and the second operating position ensuring partial cylinder shut-off at the adjusting cams for the cylinder shut-off and continuous cylinder operation in the case of the adjusting cams for the continuous cylinder operation.
In order to make the phasing operation which is known from the prior art possible, it is provided in one advantageous embodiment that two adjusting cams are provided on the control shaft per cylinder of the internal combustion engine. The geometry and arrangement in the circumferential direction of the adjusting cams on the control shaft can be adapted individually, in order to ensure a dedicated opening characteristic for each inlet valve of each cylinder.
Furthermore, the invention relates to a camshaft adjusting unit for an internal combustion engine having a camshaft with a plurality of cams which are spaced apart axially, a plurality of transmission devices which are configured to transmit a camshaft rotation and action of the cams into a translational movement to engine inlet valves which belong in each case to the transmission devices, in order to open and to close said engine inlet valves. It is possible for a position of the transmission devices and therefore their action on the inlet valves to be adapted by way of an above-described control shaft, by their adjusting cams acting on in each case one transmission device, the adjusting cams for the cylinder shut-off in the shut-off section of the cam circle being without action on the transmission device. The result is that said transmission devices do not bring about opening of the inlet valves in the case of being loaded by way of the cams of the camshaft, the control shaft having a stop which limits the rotation in both circumferential directions and serves as a calibration point for an engine electronics system. All of the features which are described above for the control shaft can be applied and are valid directly for the camshaft adjusting unit.
The invention also includes the corresponding method for shutting off inlet valves in an engine using the described camshaft adjusting unit, the position of the transmission devices and therefore their effect on the inlet valves being adapted by virtue of the fact that their adjusting cams act on in each case one transmission device, the adjusting cams for the cylinder shut-off in the shut-off section in the cam circle being without action on the transmission device. The result is that said transmission devices do not bring about opening of the inlet valves in the case of being loaded by way of the cams of the camshaft.
The invention is particularly advantageous for a straight six cylinder internal combustion engine, in which three of the six cylinders are to be shut off. A straight six cylinder internal combustion engine according to the invention includes the above-described camshaft adjusting unit, and is distinguished by the fact that three of the six cylinders can be shut off by virtue of the fact that the adjusting cams for the cylinder shut-off in the shut-off section in the cam circle are without action on the transmission devices of the three cylinders to be shut off. The result is that the transmission devices do not bring about opening of the inlet valves of the three cylinders to be shut off if they are loaded by way of the cams of the camshaft.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.